1. Field of the Invention
The invention relates to a mounting and driving structure for an auxiliary apparatus of an internal combustion engine and, more particularly, relates to a mounting and driving structure of an oil pump of a V-shaped internal combustion engine.
2. Description of the Prior Art
Among internal combustion engines for vehicles, there are engines in which the cylinders are arranged in series (in-line engines), engines in which the cylinders are arranged so as to face each other (opposed cylinder engines), engines in which banks of cylinders are arranged in a V-shape, and the like.
V-shaped internal combustion engines in which two banks of cylinders are arranged in a V-shape are constructed in a manner such that first and second cylinder heads are mounted on first and second cylinder banks of a V-shaped cylinder block, and a rotatable crank shaft is provided in the cylinder block so as to extend in the front-to-rear direction of the internal combustion engine. In one type of V-shaped engine, the front edge surface of the first cylinder head projects to a position in front of the front edge surface of the second cylinder head in the axial direction of the crank shaft. First and second rotatable cam shafts are provided for the first and second cylinder heads, first and second cam sprockets are provided in the same plane on corresponding end portions of the first and second cam shafts on the front side of the V-shaped internal combustion engine, a sprocket for a timing chain is provided on a crank shaft end portion of the crank shaft on the front side of the V-shaped internal combustion engine in the same plane as the first and second cam sprockets, and a timing chain is wound around the sprocket for the timing chain and the first and second cam sprockets.
In V-shaped internal combustion engines, an oil pump is provided as an auxiliary apparatus in order to circulate oil from an oil pan to the working parts of the engine that require lubrication. The oil pump is directly attached to the end portion of the crank shaft which projects to a position in front of the internal combustion engine so that the oil pump is directly driven by the crank shaft. Alternatively, the oil pump is driven either (1) by a timing belt or chain which is wound around the pulley or sprocket for the timing belt or chain, which pulley or sprocket is fixed to the end portion of the crank shaft, or (2) by gear mechanism coupled to the crank shaft, or (3) by a chain for the oil pump, which chain is wound around the sprocket for driving the oil pump, which sprocket is provided on the side of the end portion of the crank shaft.
Such driving structures for an auxiliary apparatus of an internal combustion engine have been disclosed in, for instance, Japanese Utility Model Registration No. 63-174513 (1988) and Japanese Utility Model Registration No 1-148031 (1989). According to the driving structure disclosed in Japanese Utility Model Registration No. 63-174513 (1988), an oil pump cover is attached to a chain cover from the side of a chain chamber to thereby form a pump chamber, and an oil pump formed with a saucer-shaped projecting portion, which portion extends to a lower portion of a sprocket which sprocket is attached to a crank shaft and around which a chain is wound, is attached to the oil pump cover. According to the driving structure disclosed in Japanese Utility Model Registration No. 1-148031 (1989), a pulley to drive another auxiliary apparatus is provided on the engine side of a motive power side variable speed pulley in which a centrifugal mechanism is arranged on the side remote from the engine, a driven side variable speed pulley in which a centrifugal mechanism is arranged on the engine side is provided at a position which is away from the drive shaft of the auxiliary apparatus, which apparatus is driven through the variable speed pulley, and an intermediate pulley for propagating and coupling to the drive pulley on the drive shaft is provided on the outer periphery of the centrifugal mechanism of the driven side variable speed pulley.
Hitherto, however, in the structure for attaching the oil pump of the V-shaped internal combustion engine, there is the inconvenience that when the oil pump is directly attached to the crank shaft, the oil pump is arranged on the axis of rotation of the crank shaft, so that the entire length of the internal combustion engine is increased and the mechanical loss is large.
In the structure in which the oil pump is driven by the timing belt, on the other hand, there is the inconvenience that the attaching position of the oil pump is high so that it takes a long time until the oil pump completely discharges the oil upon starting at a low temperature, but also it is disadvantageous because of the chain sound.
In the structure in which the oil pump is driven by the gear mechanism, moreover, there is the inconvenience that gear sounds are generated.
In the structure in which the oil pump is driven by the chain for the oil pump, on the other hand, there is the inconvenience that the sprocket for driving the oil pump is provided on the crank shaft end portion formed by extending the crank shaft in the axial direction, so that the crank shaft is substantially long and the entire length of the internal combustion engine is large.
As another structure for attaching an oil pump to an engine, there is the structure disclosed in Japanese Utility Model Registration No. 57-114116 (1982). In that structure, a stiffener having at least four legs is fixed to a lower surface of a partition wall of a crank casing by bolts, the oil pump is attached to the stiffener, and the oil pump communicates with the crank casing through an oil discharging conduit formed in the stiffener.
In the conventional attaching structure of an oil pump of an engine, when the oil pump is attached to the cylinder block of the engine, various connecting members, such as reinforcing members, stiffeners, and the like, are used thereby assuring rigidity and strength.
There are, however, the inconveniences that (1) because the number of parts is increased when the oil pump is attached to the engine, the costs are increased, that is, it is economically disadvantageous, and (2) the efficiency of the operation for attaching the oil pump is reduced, that is, it is disadvantageous from a practical point of view. There is also the inconvenience that when the oil pump has been attached, the engine size is increased due to various members, and there is a fear that it will be necessary to change the engine design so as to enlarge the oil pan surrounding the oil pump.